The present invention is a medical product that can be used to correct vision loss or even complete blindness caused by certain retinal diseases. A variety of retinal diseases cause vision loss or blindness by destruction of the vascular layers of the eye including the choroid and choriocapillaris, and the outer retinal layers including Bruch's membrane and retinal pigment epithelium. Loss of these layers is followed by degeneration of the outer portion of the inner retina beginning with the photoreceptor layer. Variable sparing of the remaining inner retina composed of the outer nuclear, outer plexiform, inner nuclear, inner plexiform, ganglion cell and nerve fiber layers, may occur.
Prior efforts to produce vision by stimulating various portions of the retina have been reported. One such attempt involved an externally powered photo-sensitive device with its photoactive surface and electrode surfaces on opposite sides. The device theoretically would stimulate the nerve fiber layer via direct placement upon this layer from the vitreous body. The success of this device is unlikely due to it having to duplicate the complex frequency modulate neural signals of the nerve fiber layer. Furthermore, the nerve fiber layer runs in a general radial course with many layers of overlapping fibers from different portions of the retina. Selection of appropriate nerve fibers to stimulate to produce formed vision would be extremely difficult, if not impossible.
Another prior device involved a unit consisting of a supporting base onto which a photosensitive material such as selenium is coated. This device was designed to be inserted through an external scleral incision made at the posterior pole. It would rest between the sclera and choroid or between the choroid and retina. Light would cause a potential to develop on the photosensitive surface producing ions which would then theoretically migrate into the retina causing stimulation. However, having no discrete surface structure to restrict the directional flow of charges, lateral migration and diffusion of charges would occur thereby preventing any resolution capability. Placement of this device between the sclera and choroid would also result in blockage of discrete ion migration to the photoreceptor and inner retinal layers. This is due to the presence of the choroid, choriocapillaris, Bruch's membrane and the retinal pigment epithelial layer all of which would block passage of these ions. Placement of the device between the choroid and the retina would still interpose Bruch's membrane and the retinal pigment epithelial layer in the pathway of discrete ion migration. As this device would be inserted into or through the highly vascular choroid of the posterior pole, subchoroidal, intraretinal and intraorbital hemorrhage would likely result along with disruption of blood flow to the posterior pole. One such device was reportedly constructed and implanted into a patient's eye resulting in light perception but no formed imagery.
The present inventor reported a design for a subretinally placed photovoltaic device comprised of multiple surface electrode microphotodiodes (SEMCPs) deposited on a single silicon crystal substrate. These SEMCPs transduce light passing through a semitransparent electrode surface onto the photoactive surface into small electric currents which stimulate overlying and surrounding inner retinal cells. Due to the solid nature of the substrate onto which the SEMCPs were placed, blockage of nutrients from the choroid to the inner retina occurs. Even with fenestrations of various geometries, permeation of oxygen and biological substances is not optimal.